In addition to the use in vehicles and aircraft, the general-purpose gasoline engine is the reciprocated piston type gasoline engine with extensive use. Generally speaking, the gasoline engine with a power within 20 kW is a small-sized general-purpose gasoline engine that is provided in common use and featured with small volume, low mass, convenient use and operation and low price. As one of the power sources, the general-purpose gasoline engine drives general-purpose machinery, such as forestry plant protection machinery, garden machinery, generator set, building machinery and the like. The general-purpose gasoline engine is power machinery with gasoline as the fuel and is composed of a cylinder, a crank connecting rod mechanism, a gas distribution system, a gasoline supply system, a lubrication system and an ignition system. The cylinder head which provided with an intake passage and an exhaust passage is together with the cylinder to form a combustion chamber surface, thereby the cylinder head is an important component of the gasoline engine. Mixture of the gasoline as fuel and air is burnt in the combustion chamber so as to generate plenty of heat energy to be as the driving energy. The intake and exhaust of the combustion chamber as well as the parameters of the combustion chamber are necessary to guarantee the high-efficient operation of the gasoline engine.
In the prior art, the combustion chamber surface of the cylinder head usually adopts a wedge-shaped structure so that a high surface to volume ratio can be obtained. The structure is good for the installation of the other auxiliary structures, such as valve assemblies. If the combustion chamber surface structure is changed, the arrangement of the intake valve assemblies and the exhaust valve assemblies thereby is affected. In order to solve said problems, a spherical combustion chamber structure with small surface to volume ratio and good influence to the performance of the gasoline engine is provided. In order to adapt to the spherical combustion chamber structure, the intake valve and the exhaust valve are arranged obliquely. However, the combustion chamber structure is only one of the key structures which affect the operation of the gasoline engine; the intake and exhaust parameters of the intake valve and the exhaust valve also have a significant influence to the work efficiency and the discharge of the gasoline engine. Only By the adoption of the spherical combustion chamber and the obliquely arranged valve structures, the efficiency or the discharge of the gasoline engine does not necessarily to be improved.
At the present stage, along with the gradually increasing global environmental requirements, for example, the requirements for the discharge of the small-sized general-purpose gasoline engine in America reach to the standard of third stage of US Environmental Protection Agency (for short, EPA3), in order to meet the standard, a catalytic converter is necessary according to the technical condition of the existing cylinder head. For the small-sized general-purpose gasoline engine, light and convenient structure, flexibility, low production cost and low use cost thereof are the advantages to occupy the market, but the use of the external purification means, such as the catalytic converter, may obviously cause a cost increase of the gasoline engine for the middle- and small-sized gasoline engine, which makes said gasoline engine lose the competitive advantage in the market as well as cause the increase of the volume and weight which makes the gasoline engine lose the advantages of handiness and flexibility. Moreover, for the catalytic converter as an external purification means, the combustion efficiency of the engine body will not be improved, and the waste gas is processed passively; and for the energy, the purpose of conservation and rational use is not realized, but the great increase of the use cost and the maintenance cost may be caused.
Therefore, an improvement for the combustion chamber surface of the cylinder head of the gasoline engine is needed, a change is made for the parameter corresponding relationship among the combustion chamber, the intake valve and the exhaust valve in the prior art, and the parameters are inter-coordinated and matched so that it is better for the mixing and combustion of the combustion gas, the improvement of the operation efficiency of the gasoline engine, the conservation of the fuel, and the reduction of the discharge. Without using the external purifying means, such as the catalytic converter, the discharge index thereof can reach to, even far higher than the requirements of the standard of the EPA3 stage. Meanwhile, the gasoline engine can keep the advantages of low cost, flexibility as well as low and convenient use and is in accordance with the market demand.